Fluorescent film with luminescent particles

ABSTRACT

A fluorescent film for use with a low-pressure discharge lamp is formed as a silicone elastomer in which luminescent particles are embedded. The film is formed by the steps of (a) mixing a hydroxyl polydiorganosiloxane with an organohydrogen siloxane, (b) adding luminescent particles, and (c) generating a chemical reaction by means of a platinum catalyst at room temperature.

This is a U.S. national stage of application No. PCT/DE00/03155, filedon 07 Sep. 2000. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b)is claimed from German Application No. 199 46 125.2, filed 20 Sep. 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to a fluorescent foil or film, particularlyfor use with a low-pressure discharge lamp, a method for producing thefluorescent film and an irradiation arrangement with the fluorescentfilm.

2. Description of the Related Art

Light absorption through the skin causes tissue changes by influencingthe neuronal, lymphatic, vascular and immune systems. This brings aboutanalgesic, antiinflammatory, antiedematous effects and stimulateshealing of wounds. A considerable increase in fibroblasts of scar tissuewas found under irradiation by red light (660 nm, 2.4-4 J/cm²) (C. Webb;M. Dyson, et al., Lasers in Surgery and Medicine, 22(5), 294-30,(1998)). When peripheral lymphocytes were irradiated by an He-Ne laserwith irradiation doses of between 28 and 112 J/m², there was an increasein RNA synthesis after stimulation of the lymphocytes bycytohemoagglutinin (N. K. Smol'yaninova, T. I. Karu, et al., BiomedicalScience, 2(2), 121-126 (1991)). With bone injuries, a doubling ofcalcium incorporation at the injury site was observed after He—Ne laserirradiation (T. Yaacoby, L. Maltz, et al., Calcified TissueInternational 59(4), 297-300, (1996)). Various chronic joint diseasessuch as gonarthrosis, LWS arthrosis and algodystrophy in hemiplegicstroke patients were found to be positively affected by He-Ne laserirradiation in over 400 patients (S. Giavelli, G. Fava, et al.,Radiologia Medica, 95(4), 303-309, (1998)). The release ofinterleukin-1-alpha and interleukin-8 has been discussed as a possiblecause for the positive effects (H. S. Yu, K. L. Chang, et al., Journalof Investigative Dermatology, 107(4), 593-596, (1996)). Irradiation at1.5 J/cm² resulted in a concentration-dependent simulation ofinterleukin- 1-alpha production and corresponding mRNA expression. Sincethese cytokines stimulate both mobility and proliferation ofkeratinocytes, it is likely that these mechanisms directly promote woundhealing. Further, models of photonic cellular energy transfer inrelation to the respiratory chain are being discussed (L. Wilden, R.Karthein, Journal of Clinical Laser Medicine and Surgery, 16(3),159-165, (1998). The biochemical models of cellular energy transfer takeinto account only the typical corpuscular aspect of electrons asresponsible for energy transfer and ignore the wave-particle dualism ofelectrons in energy transfer. The light of the red and near-infraredspectra closely corresponds to characteristic energy planes andabsorption rates of important components of the respiratory chain. Forexample, an increase in mitochondrial adenosine triphosphate productionis brought about in this way. Interactions in the red and near-IR rangescan be explained on the basis of this interaction.

Photobiological effects in the non-UV range based on an interactionbetween endogenic or exogenic chromophores in the skin are becomingincreasingly important because therapeutic effects can be influenced bymeans of suitable radiation sources in certain inflammatory skindiseases and, for example, impairment of wound healing in diabetesmellitus.

Because their efficiency is usually better than that of high-pressurelamps or temperature radiators, low-pressure discharge lamps are usedincreasingly in many technical fields, especially when high light energyefficiency is required. Single-base or double-base low-pressuredischarge lamps are known depending on the field of use. Further, theselow-pressure discharge lamps can be constructed with or withoutluminescent material and with different gases. However, all embodimentforms have in common that the light energy transfer increases as thediameter of the enveloping body decreases.

According to one model calculation, the light energy density correspondsto approximately one fourth of the quotient of the column capacity andprojection surface. This means that the theoretical maximum value of a38-mm low-pressure discharge lamp is approximately 45 mW/cm². In a 26-mmlow-pressure discharge lamp, the light energy density increases toapproximately 50 mW/cm². Theoretical light energy densities of 100, 125and 170 mW/cm² result for lamp diameters of 16 mm, 12 mm and 8 mm. Theincreased luminous density of small radiators is utilized, for example,in the construction of compact lamps having, e.g., a wall diameter of 12mm. Fluorescent tubes with a diameter of 8 mm have been in use for someyears for effect illumination. They surpass compact lamps with respectto luminous density, but the greatest available lengths are only about30 cm.

In spite of the increased light output, however, the reduction in lampgeometry has grave disadvantages. A large number of lamps with anequally large number of expensive ballast devices are required in orderto generate radiating surfaces. The lengthening of the lamps is subjectto plasma-physical limits because the high ignition voltages that arerequired for large lengths represent a considerable expenditure. Addedto this is the manufacturing cost itself, i.e., elutriation, pumping andbasing of each individual fluorescent tube.

Therefore, low-pressure discharge lamps with external or internalreflectors are usually used for surface illumination; for example, lightenergy densities of between 22 and 28 mW/cm² at an irradiation level of100 W can be achieved. However, the light energy densities that canactually be achieved are considerably lower than in theory.

The basic problem in conventional low-pressure discharge lamps withfluorescent material and electron-emitting electrodes is the limitedperiod of use, especially with very high lamp outputs.

The principal reason for this is that reaction components of theelectrode burnup react chemically with the luminescent coating, whichleads to an aging process. Another problem is that the reactioncomponents of the electrode burnup and of the mercury vapor react withalkaline compounds of the glass tube to form various amalgams. Thisresults in blackening of the tube, accelerated reduction of light outputand sometimes in a dramatic reduction in the useful life of the lamp.Since the useful life is already sharply limited due to the agingprocess of the luminescent coating, the use of expensive alkali-freefused silica glasses has so far been unprofitable. For medicalhigh-power radiators, the useful life may only amount to 48 hours, forexample.

Experimental application of luminescent material to the outside of thelow-pressure discharge lamp was not successful because the applicationof luminescent material in a non-inert atmosphere leads to aphotochemical oxidative degradation of the hygroscopic luminescentmaterial.

U.S. Pat. No. 5,717,282 discloses a Braun tube for monitor production inwhich a silica-containing paint with luminescent materials which isproduced by a sol-gel process is applied to the outer side of themonitor. The thickness of this phosphor coating is limited to about 0.5μm because, otherwise, cracks would result from the extensive shrinkageof the inorganic network. However, a layer of this thickness is too thinand does not have sufficient thermal stability for use in a low-pressuredischarge lamp at higher outputs.

U.S. Pat. No. 5,731,658 discloses a liquid crystal display in which aphosphor coating is applied to the inner boundary walls. The phosphorcoating comprises a UV-transparent carrier material and phosphor.Silicone oxide or organosilicates, particularly ethyl silicate, methylsilicate or isopropyl silicate, are suggested as carrier materials. Thecoating thickness that can be achieved in this way is also too small toallow for adequate embedding of luminescent material for a low-pressuredischarge lamp.

SUMMARY OF THE INVENTION

Therefore, the object of the invention is to provide a fluorescent filmwhich can be produced in sufficient thickness while exhibiting goodthermal stability, so that it is suitable for use in low-pressuredischarge lamps. Another object is to provide a flexible irradiationarrangement which can be used for a wide variety of applications.Another object is to provide a method for producing a fluorescent filmof this kind.

According to the invention, the fluorescent film is formed as a siliconeelastomer in which luminescent particles are embedded. The film isproduced by the steps of (a) mixing a hydroxyl polydiorganosiloxane withan organohydrogen siloxane, (b) adding luminescent particles, and (c)generating a chemical reaction by means of a platinum catalyst at roomtemperature.

On one hand, films of sufficient thickness with a sufficiently highconcentration of luminescent material can be produced in that thefluorescent film is formed as silicone elastomer in which theluminescent particles are embedded. Further, the luminescent particlesare crosslinked so as to be airtight and free of moisture in thesilicone elastomer, so that they are not subjected to an aging process.Silicone elastomers are UVC-transparent and have considerable advantagesover alternative UVC-transparent carrier materials. While sapphire andquartz are transparent to UVC, it is not possible to use inorganicluminescent materials as a dopant in quartz windows for reasonspertaining to the chemistry of luminescent material. Sapphire dopant isruled out from the start because of the extreme melting temperatures.Other plastics such as acrylates, transparent PVC or Teflon do not havesufficient thermal stability. However, the silicone elastomers arestable up to 250° C. and do not require emollients or other volatilesubstances that could evaporate. Because of the extended life of theluminescent material due to the fact that luminescent material can bearranged outside of the charging vessel and, therefore, no reaction canoccur with the electrode burnup, the use of alkali-free fused silica isalso acceptable, which further increases the life and quality of thelow-pressure discharge lamp.

In a preferred embodiment form, the silicone elastomer can be producedby a method in which a hydroxyl polydiorganosiloxane with anorganohydrogen siloxane to which the luminescent material particles areadded is in crystalline form. By means of a platinum catalyst, achemical reaction can be generated at room temperature leading to acomplete crosslinking in which the luminescent material particles arenot loaded due to the low process temperatures.

Hydroxyl polydiorganosiloxane comprising various polymers with a minimumviscosity of 1000 centipoise at room temperature has proven particularlysuitable, wherein the hydroxyl diorganosiloxane is preferably formed ashydroxyl polydimethylsiloxane, its copolymers, phenylmethylsiloxaneand/or polymethyl-3,3,3-trifluoropropylsiloxane.

The organohydrogen siloxane is preferably formed as silicone with atleast 2 silicon-bonded hydrogen atoms per molecule, particularlyhomopolymers, copolymers or mixtures thereof.

The platinum catalyst can comprise a platinum salt, particularlyplatinum chloride or chloroplatinic acid, the latter preferably beingused as a hexahydrate or in anhydrous form.

The thickness of the fluorescent film is preferably between 10 and 800μm, wherein the surface density is between 1 and 20 mg/cm². A thicknessbetween 100 and 600 μm with a surface density between 3 and 6 mg/cm²appears particularly advantageous.

An irradiation arrangement with very flexible handling can beconstructed by arranging the fluorescent film outside the dischargespace. For one, the life of the irradiation arrangement depends onlyupon the low-pressure discharge lamp itself, particularly itselectrodes, since the fluorescent films themselves can easily beexchanged at any time. Further, this enables outfitting with differentlydoped fluorescent films in a very simple manner, so that differentspectral ranges and irradiation intensities can be adjusted with oneirradiation arrangement.

In a preferred embodiment form, a displacement body is arranged in theenveloping body, so that channels are formed between the enveloping bodyand displacement body, so that the low-pressure discharge lamp can beconstructed so as to be very long without requiring very high ignitionvoltages, since there is still a sufficiently large plasma volume. Onthe other hand, the emitted light energy density increases in thechannels between the enveloping body and the displacement cylinderbecause the channel acts like a low-pressure discharge lamp with a smalldiameter. When the enveloping body and displacement body are constructedas cylinders, a cylindrical jacket is formed as a channel which can bevisualized as many low-pressure discharge lamps of small diameterarranged radially with respect to one another.

In a preferred embodiment form, the displacement body is constructed asa closed hollow body which is particularly advantageous with respect toweight.

A reflector layer can also be arranged on the outer side of thedisplacement body or the displacement body can comprise a material whichis transparent to the emitted radiation. Further, it is also possible tocombine the steps.

In order to produce low-pressure discharge lamps with different lightenergy densities, a fastening device can be used to receive differentdisplacement bodies. For production, different diameters of thedisplacement body are used depending on the desired light energydensity.

In certain applications, it is desirable to obtain uniform light energydensity over the entire irradiation surface. For sunbathing, forexample, a stronger radiation may be desired only in the head area. Thiscan easily be achieved, for example, in that the displacement body onlyextends over the head area or in that the displacement body hasdifferent diameters in longitudinal direction. A further possibilityconsists in coating the displacement body with a reflector layer atdesired places.

The possibility of operating different screen-like irradiation filmswith different luminescent materials with one and the same light sourceresults in a very multifaceted therapeutic and irradiation system. Thetreating physician can treat a different patient or replace an oldsilicone module in a very short amount of time, i.e., in a minute, bychanging the silicone module similar to the use of a large opticalfilter.

The invention will be described more fully in the following withreference to a preferred embodiment example.

BRIEF OF THE DRAWINGS

FIG. 1 shows a schematic top view of an irradiation arrangement;

FIG. 2 shows a schematic partial top view of a low-pressure dischargelamp;

FIG. 2A shows an enclosure having interchangeable covers carrying afluorescent film;

FIG. 3 shows spectra of different fluorescent films;

FIG. 4 is a graph showing intensities over film thickness;

FIG. 5 is a graph showing intensities over the surface density of theluminescent particles; and

FIG. 6 shows spectral absorption curves of a fluorescent film withvariation in time.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 shows a schematic top view of an irradiation arrangement 1 forcosmetic and/or therapeutic treatment of a patient 2. The irradiationarrangement 1 comprises at least one low-pressure discharge lamp 3, areflector screen 4 and a fluorescent film 5 which is supported so thatit can be wound on and off by means of rollers 6. The distances shownbetween the low-pressure discharge lamp 3 and the reflector screen 4 andfluorescent film 5 are not true to scale. The UV radiation generated inthe discharge program of the low-pressure discharge lamp 3 exitsisotropically from the UV-transparent enveloping tube 7 of thelow-pressure discharge lamp 3 and impinges in part directly on thefluorescent film 5. Another portion of the radiation impinges on thereflector layer 4 and is partially reflected from the latter to thefluorescent film 5. The UV radiation impinging on the fluorescent film 5partially excites the luminescent particles embedded in the fluorescentfilm 5 which then emit in the desired spectral range and irradiate thepatient. Various types of irradiation arrangements 1 can be realized bymeans of the rollers 6 onto which a portion of the fluorescent film 5 iswound.

In the simplest case, the rollers 6 extend over the full height of theirradiation arrangement 1 on which a uniformly doped fluorescent film 5is wound. Then, in case the luminescent material located in thewound-off area should be aged, this area is wound up and an unusedportion of fluorescent film 5 is wound off. Further, it is also possibleto use fluorescent films 5 with different doping, so that a determinedregion of the fluorescent film 5 with the appropriate doping dependingon the desired irradiation therapy is wound off. Further, it is possibleto provide different rollers 6 along the height, so that the variationdescribed above can also be carried out for different body parts.

FIG. 2 shows a preferred embodiment form of a low-pressure dischargelamp 3 in a schematic partial top view. The low-pressure discharge lamp3 comprises an enveloping body 7, a base 8 hermetically closing theenveloping body 7, an incandescent spiral filament 9 with contacts 10guided through the base 8 and a displacement body 11 constructed as ahollow body. The displacement body 11 is arranged so as to berotationally symmetric with respect to the enveloping body 7 and at adistance from the spiral filament 9. A reflecting coating 12 is arrangedon the outer side of the displacement body 11. A rotationally symmetricchannel 13 with the low-pressure plasma is formed between the envelopingbody 7 and the displacement body 11, wherein mercury with argon ispreferably used as filling material. Electrons are emitted via thespiral filament 9 by thermal emission and are accelerated by an externalelectrical field. This brings about an interaction with the mercuryatoms in the channel 13. The electrons of the mercury are excited by theinteraction and give off the absorbed energy again by means ofspontaneous emission of photons. The resulting UV radiation then exitsthe enveloping body 7 directly or after being reflected at the coating12 and excites the luminescent particles in the fluorescent filmarranged outside the low-pressure discharge lamp 3.

FIG. 2A shows an enclosure for the discharge lamp, which includes aframe 20 having interchangeable covers 22, 24, 26, each cover having arespective fluorescent film 23, 25, 27 with particles which are excitedby radiation from the lamp. FIG. 3 shows the intensities of differentfluorescent films with different film thickness and different dopantconcentrations for a luminescent material LS 635. The fluorescent films5 a-e have the following parameters:

Film thickness Doping Surface density of the luminescent Film (mm)(g/cm³) material particles (mg/cm³) 5a 0.2 0.2 4 5b 0.55 0.1 5.5 5c 0.60.2 12 5d 0.25 0.5 12.5 5e 0.65 0.3 19.5

FIGS. 4 and 5 show the fluorescent films 5 a-e with a standardizedintensity over the film thickness and surface density of the luminescentparticles. As will be seen particularly from FIG. 5, there are highintensities in the range of 4-6 mg/cm² surface density of theluminescent particles. Further, it will be seen, referring tofluorescent film 5 e, for example, that especially thick films with highdoping do not lead to high intensities, which is presumably to becredited to the vignetting effect and self-excitation. The presentmeasurements lead to the conclusion that an optimum exists with respectto film thickness and surface density, presumably dependent on theluminescent material, which must presumably be empirically determined.However, it is obvious from FIG. 5 that the essential parameter is thesurface density of the luminescent particles because films 5 a and 5 b;5 c and 5 d behave virtually identically in spite of considerabledifferences in thickness.

Therefore, in principle, thin films appear more suitable because theyrequire considerably less material for the same intensity, but theirtemperature stability and life compared with thicker films must bestudied in greater depth.

FIG. 6 shows the spectral UV absorption curve 20 of a fluorescent filmwith a thickness of 530 μm. Further, the UV absorption curve 21 of thisfilm after 5 days continuous loading by a 54 W UV lamp at a distance of2 cm is 60° C. and the UV absorption curve 22 after 7 days of continuousloading by a 54 W UV lamp is 60° C., where the film lay directly on theenveloping tube. These curves are an impressive demonstration of thelong life of the film, whose absorption curve also remains virtuallyunchanged even with continuous loading.

1. A fluorescent film formed as a silicone elastomer in which hydroxylpolydiorganosiloxane and organohydrogen siloxane are cross-linked and inwhich luminescent particles are embedded.
 2. A fluorescent filmaccording to claim 1, wherein the hydroxyl polydiorganosiloxanecomprises various polymers with a minimum viscosity of 1000 centipoiseat 25° C.
 3. A fluorescent film according to claim 2, wherein thehydroxyl polydiorganosiloxane is formed as at least one of hydroxylpolydimethylsiloxane, its copolymers, phenylmethylsiloxane andpolymethyl-3,3,3-trifluoropropylsiloxane.
 4. A fluorescent filmaccording to claim 2 wherein the organohydrogen siloxane is formed assilicone with at least two silicon-bonded hydrogen atoms per molecule.5. A fluorescent film according to claim 4 wherein the organohydrogensiloxane comprises one of homopolymers, copolymers, and mixturesthereof.
 6. A fluorescent film according to claim 1 wherein thefluorescent film has a thickness between 10 and 800 μm.
 7. A fluorescentfilm as in claim 1 wherein the luminescent particles have a surfacedensity which is between 1 and 20 mg/cm².
 8. A fluorescent filmaccording to claim 1 wherein the luminescent particles have a grain sizewhich is between 5 and 15 μm.
 9. An irradiation arrangement comprising:a low-pressure discharge lamp with an enveloping body which istransparent to UVC, and electrodes which can be contacted from theoutside projecting into the enveloping body, and a fluorescent filmformed as a silicone in which elastomer hydroxyl polydiorganosiloxaneand organohydrogen siloxane are cross-linked and in which luminescentparticles are embedded.
 10. An irradiation arrangement according toclaim 9, wherein the fluorescent film is applied to an outer surface ofthe enveloping body.
 11. An irradiation arrangement according to claim10 wherein fluorescent films with different doping are applied to theenveloping body.
 12. An irradiation arrangement according to claim 9further comprising a displacement body arranged in the enveloping body,so that channels are formed between the enveloping body and displacementbody.
 13. An irradiation arrangement according to claim 12, wherein thedisplacement body is constructed as a closed hollow body.
 14. Anirradiation arrangement according to claim 12 further comprising areflector layer applied to an outer surface of the displacement body.15. An irradiation arrangement according to claim 12 wherein thedisplacement body comprises a material that is transparent to radiationemitted by the discharge lamp.
 16. An irradiation arrangement accordingto claim 9 wherein the fluorescent film is fitted to the enveloping bodyin the form of an interchangeable frame.
 17. An irradiation arrangementaccording to claim 9, further comprising a dispensing roller and atake-up roller on which the fluorescent film is wound up, whereby filmswith different doping can befitted to the enveloping body.
 18. A methodfor producing a fluorescent film formed as a silicone elastomer in whichluminescent particles are embedded, comprising the following steps: (a)mixing a hydroxyl polydiorganosiloxane with an organohydrogen siloxane,(b) adding luminescent particles, and (c) generating a chemical reactionby means of a platinum catalyst at room temperature.
 19. A method forproducing a fluorescent film according to claim 18, wherein the hydroxylpolydiorganosiloxane comprises various polymers with a minimum viscosityof 1000 centipoise at 25° C.
 20. A method for producing a fluorescentfilm according to claim 19, wherein the hydroxyl polydiorganosiloxane isformed as at least one of hydroxyl polydimethylsiloxane, its copolymers,phenylmethylsiloxane, and polymethyl-3,3,3-trifluoropropylsiloxane. 21.A method for producing a fluorescent film according to claim 18 whereinthe organohydrogen siloxane is formed as silicone with at least twosilicon-bonded hydrogen atoms per molecule.
 22. A method for producing afluorescent film according to claim 21 wherein the organohydrogensiloxane comprises one of homopolymers, copolymers, and mixturesthereof.
 23. A method for producing a fluorescent film according toclaim 18 wherein the platinum catalyst comprises one of a platinumchloride, platinum salts, and chloroplatinic acid.
 24. A method forproducing a fluorescent film according to claim 23, wherein thechloroplatinic acid is in the form one of a hexahydrate and anhydrouschloroplatinic acid.